The use of numerically-controlled machines for repetitive machining operations has gained wide acceptance in American industry. The numerical-controlled machines are programmed to do repetitive functions, which allows for relatively inexpensive manufacture of certain products. One of the problem areas encountered with a numerical-controlled machine is in the area of tapping holes. The speeds and feeds of numerical-controlled machines are generally accurate; but speeds and feeds vary, for many reasons over which there may be no control, such as, line voltage fluctuations in the electrical circuit to the machine. In certain instances, the original input of information to the control device is not entirely accurate, so that there must be allowance for some error.
There are known tap holders which are particularly adapted for use in numerical-controlled machines, which tap holders may make some adjustments and compensations for variations in materials and speeds and feeds. These devices generally are quite cumbersome and quite expensive. The known tap holders are such that they do not readily adapt themselves to automatic tool changes; and, as a result, the efficiency of a numerical-controlled machine is decreased when an operator must be on hand to watch a tapping operation or to make tool changes.